1. Field of the Invention
This invention relates to wheelchairs, particularly to power wheelchairs with enhanced curb-climbing ability for use by handicapped and disabled persons.
2. Description of the Prior Art
Power wheelchairs, and particularly mid-wheel drive power wheelchairs, are known and have been the subject of increasing development efforts to provide handicapped and disabled persons with independent mobility to assist them in leading more normal and active lives. Examples of mid-wheel drive power wheelchairs are found in U.S. Pat. Nos. D397,645; D404,693; 5,944,131; 6,129,165; 6,176,335; 6,186,252; 6,196,343; 6,199,647; and 6,341,657. While the mid-wheel drive power wheelchairs described in these patents have improved the state of the power wheelchair art over the prior motorized power wheelchairs, they all suffer from a common deficiency. They all include a resilient suspension, which is located forward of the front portion of the power wheelchair frame, for supporting the forward anti-tip idler wheels. This results in interference with the legs and feet of the handicapped person riding in the power wheelchair causing the legs and feet to be unnecessarily forwardly extended, and can result in injury to the handicapped person under certain conditions. Bumping of the users' feet due to the increased forward extension and pinching of their legs can occur because of the close proximity of their legs to the suspension assembly.
An example of an improved mid-wheel drive power wheelchair that overcomes these deficiencies is found in U.S. patent application Ser. No. 10/396,052 filed Mar. 25, 2003, the disclosure of which is incorporated herein by reference. In this improved design the resilient suspension system for supporting the forward anti-tip idler wheels is located no further forward than the front portion of the power wheelchair frame.
In prior designs of mid-wheel drive power wheelchairs the forward anti-tip idler wheel(s), castor wheel(s) or other anti-tip devices are resiliently mounted to the frame and/or rigidly connected to the drive motor(s). Any design without a resilient suspension on the anti-tip device results in a compromise in choosing between the possibility of forward tipping of the power wheelchair or the ability of the power wheelchair to climb over obstacles.
A resilient suspension for the anti-tip device is therefore preferred in mid-wheel design power wheelchairs. In some models it is also preferred to have the anti-tip device attached to the drive wheel to assist the power wheelchair in climbing over obstacles. In these designs the drive motors are preferably pivotally connected to the frame and are controlled by a resilient suspension attached between the drive motor and the frame. This suspension design also is dictated by the weight of the power wheelchair and the wheelchair occupant.
In prior designs where the anti-tip device is connected to the motor using a resilient suspension, this resilient suspension controls the movement of the anti-tip device which is indirectly connected to the power wheelchair frame. In this configuration upward movement of the anti-tip device compresses the resilient suspension. Compressing the resilient suspension reduces the force applied that causes movement of the drive motor. Additionally, it takes more force to raise the anti-tip device or lower the drive wheel. In this configuration the drive motor and anti-tip device cannot move independently.
Handicapped persons needing power wheelchairs have a variety of problems with their legs and feet, such as having little or no sensation in them. Having the suspension assemblies, consisting of spring/strut combinations that are designed to compress and expand, in proximity to the user's legs could cause pinching of the clothing or skin of the user. In addition the anti-tip arm on the prior power wheelchairs forces the spring and strut upward and could cause injury to the user. The potential liability for such injuries can be substantial.
Even if the resilient suspension assemblies are covered by fenders having integral bumper members lying over and protecting them, the handicapped person's legs and feet must necessarily be extended forward and/or inward to accomodate the space taken up by the suspension assemblies. This causes the overall length of the power wheelchair occupant's footprint to increase, resulting in a greater turning radius and less maneuverability in tight areas and making the power wheelchair less practical. There are also limitations placed on the hardware available that can be used to support the person's legs and feet due to the suspension assemblies being positioned forward of the front portion of the power wheelchair frame. The width of the footrest that can be folded upward between the assemblies is decreased, and the flexibility in mounting individual leg rests with regard to the height and angle is also decreased.
Another deficiency of the prior power wheelchairs involves the aesthetics. Several components of the prior power wheelchairs such as the moving springs and spring struts must be covered by the body and fenders that extend beyond the front of the frame. These body/fender components are generally molded from plastic in an injection molding or vacuum forming process, and the required forward extending fenders must be stretched at the corners, thus presenting problems in the manufacturing process. A more aesthetically pleasing, as well as functional, body would extend only as far as the front portion of the power wheelchair frame. Such a streamlined body would be easier to manufacture because of fewer curves and radiuses.